The present invention relates to the field of explosives, and more particularly relates to particles of an explosive and a process for obtaining such particles.
There exists explosive particles, such as, for example, nitramines (RDX, HMX etc.) or CL20, that have a variable sensitivity to shock. It is also known that for conventional nitramines (RDX, HMX), the lowest sensitivity of explosive formulations to shock is obtained with particles of very small sizes, typically particles having sizes between 0 and 10 μm. However, the use of these very small particles in cast formulations is difficult because of the high viscosity of the mixtures.
In the context of these formulations, it is also preferable to use particles having sizes greater than 100 μm in order to reduce the viscosity of the mixtures. However, the exposure to the risk of explosion is greater as size of the particles increases, the higher the sensitivity to shock.
U.S. Pat. No. 4,065,529 describes a process that enables the viscosity of particles to be reduced. The process consists of treating the particles by stirring and partial dissolving to render them spherical, this process being carried out on particles having a size greater than 70 μm.
Techniques that enable the sensitivity of nitramines to shock are furthermore known. U.S. Pat. No. 6,603,018 describes the synthesis of a nitramine compound that contains one or more N-heterocyclomethyl functions that give it high energy performances while rendering it less sensitive to shock than nitramines, which do not have such functions.
U.S. Pat. No. 6,194,571, which, in this same point of view, proposes the synthesis of the alpha-HMX structure, which is less sensitive to shock than the beta-, delta- and gamma-HMX crystalline structures.
U.S. Pat. No. 6,428,724 moreover proposes coating and agglomeration of elementary particles of nitramines in the form of granules to facilitate the use in explosive formulations, in particular, if the elementary particles are elongated in shape. Coating is a conventional technique for reducing the sensitivity of explosive formulations to shock, but this does not reduce the intrinsic sensitivity of elementary particles.
The document “Optimization of batch cooling crystallization” by Choong and Smith published in Chemical Engineering Science, describes a process for the preparation of crystalline particles by nucleation and crystalline growth consisting of cooling a supersaturated solution of a product suitable for formation of these particles with a cooling in t4 without seeding and in t3 with seeding.
However, this process enables the size of the particles to be controlled, but the particles have numerous internal defects. The use of this process for the preparation of explosive crystalline particles would lead to particles having a high sensitivity to shock being obtained.
EP 1256558 describes a method for the preparation of crystalline particles by nucleation and crystalline growth consisting of cooling, in the presence of ultrasound, a supersaturated solution of a product suitable for formation of these particles with a cooling of the order of 0.3° C./min. The presence of ultrasound enables the control of the size of the particles to be improved, in particular a reduction in the width of the size distribution, and enables the need for seeding and therefore the defects and gaps which appear at the renewal of a growth on the nuclei used for the seeding to be avoided. However, this process enables neither suppression nor limitation of defects due to inclusions of solvent, which are the main defects observed both with a process according to Choong and with a process according to EP 1256558. The particles obtained thus have a significant sensitivity to shock.